A key element in an optical communication system is a photodetector. The efficiency of a photovoltaic cell or light detector is measured by a quantity referred to as the “external quantum efficiency.” In general, external quantum efficiency is not constant across all wavelengths. In particular, for many photovoltaic and light detecting devices, there is a sharp drop in external quantum efficiency as wavelength surpasses about 1000 nm. Thus, much of this energy cannot be captured for use or detection.
Known silicon photodetectors do not respond efficiently at shorter wavelengths, for example between 700 nm and 900 nm. However, as the wavelength extends past about 1000 nm, the external quantum efficiency of known silicon photodetectors begins to plummet.
A particularly common light source used in optical communication systems is the Nd:Yag laser. This laser outputs a beam at 1064 nm. Unfortunately, known silicon photodetectors do not respond efficiently to photons at such long wavelengths.
To some extent, it is possible to compensate for this lack of efficiency by providing a device having a thicker substrate. However, doing so comes at the cost of increasing response time. A need therefore exists for a photodetecting device with sufficiently external quantum efficiency at infrared wavelengths to avoid the need to have a thicker device, and accordingly, avoids the performance trade-offs associated with such a device.